Cardiovascular disease remains a leading cause of death in the developed world, responsible for more than 40% of deaths in Australia and in the United States. Annual diagnoses of new cases of heart failure in the United States have reached 550,000, leading to a population of approximately 4.7 million people afflicted by the disease; annual cost estimates for heart failure treatment range from USD$10 billion to $38 billion. Cardiac transplantation provides substantial benefit for patients with severe heart failure, however there is a gross disparity between the numbers of potential recipients (800,000 p. a. worldwide) and suitable transplant donors, approximately 3,000 p. a. worldwide. Consequently, there is a clear need for development of an effective heart support device.
In the past, Ventricular Assist Devices (‘VADs’) or Left Ventricle Assist Devices (‘LVADs’) have been developed to provide support to the heart and are typically used for temporary (bridge-to-transplant and bridge-to-recovery) and permanent (alternative-to-transplant) support of patients. Generally, support for the left ventricle with an assist device (rather than a total artificial heart) is sufficient to restore cardiovascular function to normal levels for patients with terminal congestive heart failure. As a consequence of the shortage of transplants, there is a focus on long term alternative-to-transplant support in device development. The initial VADs developed were pulsatile (implanted and external to the body) and these have demonstrated enhanced survival and quality of life for patients with end-stage heart failure compared with maximal medical therapy. However these devices are generally large, cumbersome, inefficient, prone to mechanical failure and costly.
It has been noted that continuous flow rotary VADs are generally simpler, smaller and more reliable, as well as cheaper to produce, than the earlier pulsatile systems. For this reason, continuous flow centrifugal devices, such as the VentrAssist LVAD, have emerged as the definitive forms of technology in the field of cardiac assistance.
A prior art implantable axial flow rotary blood pump is described in U.S. Pat. No. 5,370,509—Golding et al. This pump includes two blade sets and a support ring. The primary blade set functions as a thrust bearing to pump the blood directly from the inlet to the outlet. The secondary blade set functions to divert blood around the outer surface of the impeller. This diversion of blood is forced through a radially extending restriction. The effect of which is to create a fluid bearing that suspends the impeller only in the axial direction. The pump disclosed within this document has two main disadvantages.
The first disadvantage is that the blood paths disclosed in that document are not perfected. The subsidiary blood flow around the impeller is pushed in the same direction as the primary blood flow through the middle of the impeller. This type of blood path requires relatively high energy to maintain and generally lacks efficiency.
The second disadvantage is that secondary blade set may induce thrombogenesis and/or haemolysis within the pump due their shape.
Another prior art pump is disclosed in U.S. Pat. No. 6,227,797—Watterson et al. It is a centrifugal rotary blood pump with a hydrodynamically suspended impeller. The main disadvantage with this device is that the impeller of this pump includes complex blade geometry which increases the cost of manufacturing.
U.S. Pat. No. 5,211,546—Isaacson et al., discloses an axial flow rotary blood pump wherein the impeller is only hydrodynamically suspended in the radial direction relative to the axis of rotation. Additionally, the pump disclosed therein includes a hub or spider to position the impeller. Hubs and spiders typically generate a location within the pump of blood flow stagnation. Locations or points of stagnation within the channel of blood flow should be avoided to reduce the chance or likelihood of thrombogenesis or blood clots.
U.S. Pat. No. 6,100,618—Schoeb et al. describes an axial flow pump with a simplifier motor rotor design. This pump is not suitable as an implantable blood pump design and the impeller within the pump is only radially hydrodynamically suspended.
It is an object of the present invention to address or ameliorate one or more of the above described problems of the prior art.